Dual element fuse



July 24, 1962 .1. B. WRIGHT 3,046,374

DUAL. ELEMENT FUSE Filed Oct. 12, 1959 /2 H2 /3 022 23 6 l5 l6 l7 l8 l V FIG.

22 #23 FIG. 3

l5 1 I6 s 1 r- 5 28 INVENTOR. JAMES B. WRIGHT BY 3,046,374 DUAL ELEMENT FUSE James B. Wright, Warren, Pa., assignor to Cersolsun Research Corporation, 'Warren, Pa., a corporation of Delaware Filed Oct. 12, 1959, Ser. No. 845,953 5 Claims. (Cl. 200-123) This invention relates to a new and improved circuitprotecting fuse. More particularly, the invention relates to :a new fuse structure which protects a circuit against extreme current overloads such as might be caused by a short circuit or the like, and also protects the circuit against slight overloads which persist for an extended period of time.

These dual protection fuses generally contain a circuitconduoting portion, part of which is of reduced crosssection that will fuse under extreme overload conditions such as occur in a short circuit. In addition, the fuses contain -a second circuit-conducting portion which is an enlarged mass and which is maintained as part of the conducting circuit by the use of a low melting temperature material such as a solder. Thus, even if only a slight overload occurs and is maintained, the large cross-section conductive element will absorb sufficient heat over a period of time to cause the low temperature solder to melt, which results in the breaking of the conductive circuit. This break in the circuit occurs in spite of the fact that the overload is insufficient to fuse the reduced cross-section portion of the fuse which protects against an extreme overload.

Although dual element fuses have been in widespread use for a number of years and are generally considered to be superior to conventional single element fuses, they have not been completely satisfactory in all applications.

One of the difficulties in constructing a suitable dual element fuse is the restriction on the amount of space which the fuse occupies. Thus, while certain fuse constructions are satisfactory for use in large fuses, it is not possible to reduce the size of the fuse elements to permit their use in fuses having smaller cases. Another difliculty encountered when workingwith small fuses is the lack of space in the fuse case for the required assembly operations, even if the fuse elements themselves are of a sufliciently small size. 7

One of the other problems which arises with fuse designs in which a spring is used to move the heat-absorbing conductive portion to a position which will cause a break in the circuit is the failure of operation of the fuse due to deterioration of the spring. This deteriration is generally the result of the springs being subjected to compressive or tensile forces over a long period of time, part of which may be at elevated temperatures.

Failure of the spring to move the heat-absorbing portion out of contact with the conductive circuit when a sustained overload occurs, may result in serious damage to other parts of the circuit, i.e., the leads, etc.

Arcing also may be a problem in certain fuse designs, even in cases where the spring functions properly, if the design is such that the heat-absorbing portion is prevented from being moved quickly a sufiicient distance from the conducting links.

However, by employing the fuse structure of the present invention, the aforementioned difiiculties are largely overcome. The fuse of the invention provides a simplified arrangement of fusible elements which permits its use in fuses of relatively small size, as Well as larger fuses, while providing a high degree of protection against both minor current overloads and extreme current overloads. Moreover, the design of the fuse greatly reduces the possibility of spring failure and, in addition, provides atent 3,946,374 Patented July 24, 19%2 adequate separation of the conductive portions when the circuit is supposed to be broken, so that arcing is substantially eliminated.

Gther advantages and features of the fuse structure of the present invention will become apparent from the following detailed description and drawing, in which:

FIGURE 1 is a sectional view of a fuse made in accordance with the present invention, showing the fuse in a normal position.

FIGURE 2 is a plan View of the fuse element; and

FIGURE 3 is a sectional view of the fuse element showing the element after the current has been broken, due to a slight overload which has persisted for an excessive period of time.

The fuse comprises a tubular housing 11, made of an insulating material, such as fiber, to each end of which are attached caps 12 and i3. Conductive blades 15 and 16 extend through a slot in each cap, and to the inwardly extending end of each blade are fastened axially aligned fusible link members 1'7 and 18. These link members are formed of any of the fusible materials which are commonly used in the fuse art, for example, zinc, copper, etc. Portions of either or both of the links may be weakened, or cut away, as shown in FIGURE 2 at points 29 and 21, to provide a heat generating section which will insure that fusing will take place at the weakened or cut-away areas if an excessive current overload should occur, thereby breaking the circuit.

Links 17 and 18 extend inwardly through slots cut in supports or washers 22 and 23 made of an insulating maten'al. These insulating washers hold the links in a fixed position to prevent transverse movement of the ends thereof with respect to each other and also function to restrain the arc-quenching material which fills each end cavity 34 and 35 from entering cavity 36.

Bridging the gap between the inwardly extending ends of links 17 and 13 are a pair of heat-storing conductive elements or blocks of substantial mass, 25 and 26. These blocks, which may be of copper, or other similar material, are secured to the ends of links 17 and 18 by means of a fusible material, such as a solder, placed at points 27 and 28.

Heatstoring blocks 25 and 26 are of a sufficiently large size so that heat which is generated by an overload in the circuit will be absorbed by the blocks. If the overload should continue for an extended period of time, the blocks will increase in temperature as will the low melting solder securing the blocks to the ends of links 17 and it at points 27 and 28. If sufficient heat is generated, the soider will soften and melt so that the conductive blocks may be readily separated from the ends of the links thereby interrupting the circuit.

Quick separation of blocks 25 and 26 is facilitated by the use of spring means which cause the blocks to separate abruptly and create a sizeable gap between the blocks and the links to avoid arcing. FIGURE 3 of the drawing shows the fuse when the circuit has been broken by a slight overload which has persisted for an extended period of time.

Advantageously, the spring means employed to separate the blocks is positioned adjacent to the heat-storing blocks to avoid the build-up of heat in the springs. As shown in FIGURE 1, a pair of springs 3t} and 31 are attached to the blocks 25 and 26 by means of a hole located near an end of each block. For example, spring 30 is attached to blocks 25 and 26 by means of holes 32. and 33, and in the same way, spring 31 is also attached to the opposite side of the blocks (not shown). Positioning the springs in this manner minimizes the effects of heataging and eliminates the problem of fuse failure due to deterioration of the spring.

Although it is not necessary that blocks 25 and 26 be of a particular shape or configuration, it is important that the mass of the blocks be sufficient to provide the required heat absorption characteristics. Also, it is important that the shape of the blocks be such that the blocks will move a sufficient distance when opened to insure a complete break in the circuit. Advantageously, the shape of the blocks is such that the blocks when open will press firmly against the housing 11 to prevent collapsing of the housing across links 17 and 18 which might result in the reformation of the circuit. If desired, slots may be cut in the adjoining faces of the blocks to facilitate the positioning of the blocks with respect to the link members.

It is apparent from the above description that various modifications may be made in the fuse structure described. For example, the fuse may be made as a renewable fuse, if desired, with the fusible elements being assembled in a fibrous tube with the link members extending outwardly therefrom. This subassembly unit may then be connected to the circuit by bolting or otherwise attaching the link member of the subunit to the exposed contact points in the circuit.

As shown in the foregoing description, the present invention provides a new fuse structure which protects a circuit both against extreme overloads and against light overloads which persist for an extended period of time. Also, the fuse structure of the invention provides a simplified arrangement which greatly reduces the possibility of spring failure and, in addition, provides adequate separation of the portions of the fuse so that arcing is substantially eliminated.

Since, as pointed out above, various modifications can be made within the scope of the invention, the invention is not intended to be limited to the particular fuse structure disclosed in detail herein, except as may be required by the appended claims.

What is claimed is:

1. A circuit-protecting fuse comprising a pair of fusible link members arranged in axial alignment with their inner ends spaced apart and being provided with regions of limited cross-sectional area to provide heat-generating sections, a pair of heat-storing, conductive elements each extending between said spaced inner ends of said link members and being secured thereto by a heat-sensitive material, and spring means adjacent to said conductive elements to cause a separation of the elements in an angular direction from the ends of said link members when the heat stored in said conductive elements causes said heatsensitive material to soften.

2. A circuit-protecting fuse comprising a pair of fusible link members arranged in axial alignment with their inner ends spaced apart and being provided with regions of limited cross-sectional area to provide heat-generating sections, a pair of heat-storing, conductive elements each extending between said spaced inner ends of said link members and being secured thereto by a heat-sensitive material, said conductive elements being connected to each other by spring means adjacent to said conductive elements, said spring means being attached to said conductive elements near an end portion of said conductive elements to cause a separation of the elements in an angular direction from the end of one link member when the heat stored in said'conductive elements causes said heat-sensitive material to soften.

3. A renewable circuit-protecting fuse comprising a pair of fusible link members arranged in axial alignment with their inner ends spaced apart and being provided with regions of limited cross-sectional area to provide heat-generating sections, a pair of heat-storing, conductive elements each extending between said spaced inner ends of said link members and being secured thereto by a heat-sensitive material, said conductive elements being connected to each other by a pair of springs positioned adjacent to said conductive elements, said springs being attached to said conductive elements near an end portion of said conductive elements to cause a separation of the elements in an angular direction from the end of one link member when the heat stored in said conductive elements causes said heat-sensitive material to soften.

4. A circuit-protecting fuse comprising a housing, a

, pair of fusible link members arranged in axial alignment with their inner ends spaced apart and being provided with regions of limited cross-sectional area to provide heat-generating sections, supports in saidhousing for maintaining said link members in a fixed position, a pair of heat-storing, conductive elements each extending between said spaced inner ends of said link members and being secured thereto by a heat-sensitive material, said conductive elements being connected to each other by spring means adjacent to said conductive elements, said spring means being attached to said conductive elements near an end portion of said conductive elements to cause a separation of the elements in an angular direction from the end of one link member when the heat stored in said conductive elements causes said heat-sensitive material to soften.

5. A circuit-protecting fuse comprising a housing, a pair of fusible link members arranged in axial alignment with their inner ends spaced apart and being provided with regions of limited cross-sectional area to provide heat-generating sections, supports in said housing for maintaining said link members in a fixed position, a pair of heat-storing conductive elements each extending between said spaced inner ends of said link members and being secured thereto by a heat-sensitive material, said conductive elements being connected to each other by a pair of springs positioned adjacent to said conductive elements, said springs being attached to said conductive elements near an end portion of said conductive elements to cause a separation of the elements in an angular direction from the end of one link member when the heat stored in said conductive elements causes said heatsensitive material to soften.

References Cited in the file of this patent UNITED STATES PATENTS 1,003,009 Reimann Sept. 12, 1911 2,300,142 Wood Oct. 27, 1942 2,321,711 Taylor June 15, 1943 2,542,738 Wallace et al. Feb. 20, 1951 2,613,297 Laing Oct. 7, 1952 2,727,109 Von Hoorn Dec. 13, 1955 

